package com.demo2do.core.utils;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.lang.annotation.Annotation;
import java.net.URL;
import java.net.URLDecoder;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>
 * ClasspathScanner is used to locate classes that are available in the/a class
 * path and meet arbitrary conditions. The two most common conditions are that a
 * class implements/extends another class, or that is it annotated with a
 * specific annotation. However, through the use of the {@link Test} class it is
 * possible to search using arbitrary conditions.
 * </p>
 * 
 * <p>
 * A ClassLoader is used to locate all locations (directories and jar files) in
 * the class path that contain classes within certain packages, and then to load
 * those classes and check them. By default the ClassLoader returned by
 * {@code Thread.currentThread().getContextClassLoader()} is used, but this can
 * be overridden by calling {@link #setClassLoader(ClassLoader)} prior to
 * invoking any of the {@code find()} methods.
 * </p>
 * 
 * <p>
 * General searches are initiated by calling the
 * {@link #find(ClasspathScanner.Test, String...)} ()} method and supplying a
 * package name and a Test instance. This will cause the named package <b>and
 * all sub-packages</b> to be scanned for classes that meet the test. There are
 * also utility methods for the common use cases of scanning multiple packages
 * for extensions of particular classes, or classes annotated with a specific
 * annotation.
 * </p>
 * 
 * <p>
 * The standard usage pattern for this class is as follows:
 * </p>
 * 
 * <pre>
 * ClasspathScanner&lt;ActionBean&gt; resolver = new ClasspathScanner&lt;ActionBean&gt;();
 * resolver.findImplementation(ActionBean.class, pkg1, pkg2);
 * resolver.find(new CustomTest(), pkg1);
 * resolver.find(new CustomTest(), pkg2);
 * Collection&lt;ActionBean&gt; beans = resolver.getClasses();
 * </pre>
 * 
 * <p>
 * This class was copied from Stripes -
 * http://stripes.mc4j.org/confluence/display/stripes/Home
 * </p>
 * 
 * @author Downpour
 */
public class ClasspathScanner<T> {

    private static final Logger logger = LoggerFactory.getLogger(ClasspathScanner.class);

    /**
     * A simple interface that specifies how to test classes to determine if
     * they are to be included in the results produced by the ResolverUtil.
     */
    public static interface Test {
        /**
         * Will be called repeatedly with candidate classes. Must return True if
         * a class is to be included in the results, false otherwise.
         */
        boolean matches(Class<?> type);

        boolean matches(URL resource);

        boolean doesMatchClass();

        boolean doesMatchResource();
    }

    public static abstract class ClassTest implements Test {
        public boolean matches(URL resource) {
            throw new UnsupportedOperationException();
        }

        public boolean doesMatchClass() {
            return true;
        }

        public boolean doesMatchResource() {
            return false;
        }
    }

    public static abstract class ResourceTest implements Test {
        public boolean matches(Class<?> cls) {
            throw new UnsupportedOperationException();
        }

        public boolean doesMatchClass() {
            return false;
        }

        public boolean doesMatchResource() {
            return true;
        }
    }

    /**
     * A Test that checks to see if each class is assignable to the provided
     * class. Note that this test will match the parent type itself if it is
     * presented for matching.
     */
    public static class IsA extends ClassTest {
        private Class<?> parent;

        /**
         * Constructs an IsA test using the supplied Class as the parent
         * class/interface.
         */
        public IsA(Class<?> parentType) {
            this.parent = parentType;
        }

        /**
         * Returns true if type is assignable to the parent type supplied in the
         * constructor.
         */
        public boolean matches(Class<?> type) {
            return type != null && parent.isAssignableFrom(type);
        }

        @Override
        public String toString() {
            return "is assignable to " + parent.getSimpleName();
        }
    }

    /**
     * A Test that checks to see if each class name ends with the provided
     * suffix.
     */
    public static class NameEndsWith extends ClassTest {
        private String suffix;

        /** Constructs a NameEndsWith test using the supplied suffix. */
        public NameEndsWith(String suffix) {
            this.suffix = suffix;
        }

        /**
         * Returns true if type name ends with the suffix supplied in the
         * constructor.
         */
        public boolean matches(Class<?> type) {
            return type != null && type.getName().endsWith(suffix);
        }

        @Override
        public String toString() {
            return "ends with the suffix " + suffix;
        }
    }

    /**
     * A Test that checks to see if each class is annotated with a specific
     * annotation. If it is, then the test returns true, otherwise false.
     */
    public static class AnnotatedWith extends ClassTest {
        private Class<? extends Annotation> annotation;

        /** Construts an AnnotatedWith test for the specified annotation type. */
        public AnnotatedWith(Class<? extends Annotation> annotation) {
            this.annotation = annotation;
        }

        /**
         * Returns true if the type is annotated with the class provided to the
         * constructor.
         */
        public boolean matches(Class<?> type) {
            return type != null && type.isAnnotationPresent(annotation);
        }

        @Override
        public String toString() {
            return "annotated with @" + annotation.getSimpleName();
        }
    }

    public static class NameIs extends ResourceTest {
        private String name;

        public NameIs(String name) {
            this.name = "/" + name;
        }

        public boolean matches(URL resource) {
            return (resource.getPath().endsWith(name));
        }

        @Override
        public String toString() {
            return "named " + name;
        }
    }

    /** The set of matches being accumulated. */
    private Set<Class<? extends T>> classMatches = new HashSet<Class<? extends T>>();

    /** The set of matches being accumulated. */
    private Set<URL> resourceMatches = new HashSet<URL>();

    /**
     * The ClassLoader to use when looking for classes. If null then the
     * ClassLoader returned by Thread.currentThread().getContextClassLoader()
     * will be used.
     */
    private ClassLoader classloader;

    /**
     * Provides access to the classes discovered so far. If no calls have been
     * made to any of the {@code find()} methods, this set will be empty.
     * 
     * @return the set of classes that have been discovered.
     */
    public Set<Class<? extends T>> getClasses() {
        return classMatches;
    }

    public Set<URL> getResources() {
        return resourceMatches;
    }

    /**
     * Returns the classloader that will be used for scanning for classes. If no
     * explicit ClassLoader has been set by the calling, the context class
     * loader will be used.
     * 
     * @return the ClassLoader that will be used to scan for classes
     */
    public ClassLoader getClassLoader() {
        return classloader == null ? Thread.currentThread().getContextClassLoader() : classloader;
    }

    /**
     * Sets an explicit ClassLoader that should be used when scanning for
     * classes. If none is set then the context classloader will be used.
     * 
     * @param classloader
     *            a ClassLoader to use when scanning for classes
     */
    public void setClassLoader(ClassLoader classloader) {
        this.classloader = classloader;
    }

    /**
     * Attempts to discover classes that are assignable to the type provided. In
     * the case that an interface is provided this method will collect
     * implementations. In the case of a non-interface class, subclasses will be
     * collected. Accumulated classes can be accessed by calling
     * {@link #getClasses()}.
     * 
     * @param parent
     *            the class of interface to find subclasses or implementations
     *            of
     * @param packageNames
     *            one or more package names to scan (including subpackages) for
     *            classes
     */
    public void findImplementations(Class<?> parent, String... packageNames) {
        if (packageNames == null)
            return;

        Test test = new IsA(parent);
        for (String pkg : packageNames) {
            findInPackage(test, pkg);
        }
    }

    /**
     * Attempts to discover classes who's name ends with the provided suffix.
     * Accumulated classes can be accessed by calling {@link #getClasses()}.
     * 
     * @param suffix
     *            The class name suffix to match
     * @param packageNames
     *            one or more package names to scan (including subpackages) for
     *            classes
     */
    public void findSuffix(String suffix, String... packageNames) {
        if (packageNames == null)
            return;

        Test test = new NameEndsWith(suffix);
        for (String pkg : packageNames) {
            findInPackage(test, pkg);
        }
    }

    /**
     * Attempts to discover classes that are annotated with to the annotation.
     * Accumulated classes can be accessed by calling {@link #getClasses()}.
     * 
     * @param annotation
     *            the annotation that should be present on matching classes
     * @param packageNames
     *            one or more package names to scan (including subpackages) for
     *            classes
     */
    public void findAnnotated(Class<? extends Annotation> annotation, String... packageNames) {
        if (packageNames == null)
            return;

        Test test = new AnnotatedWith(annotation);
        for (String pkg : packageNames) {
            findInPackage(test, pkg);
        }
    }

    public void findNamedResource(String name, String... pathNames) {
        if (pathNames == null)
            return;

        Test test = new NameIs(name);
        for (String pkg : pathNames) {
            findInPackage(test, pkg);
        }
    }

    /**
     * Attempts to discover classes that pass the test. Accumulated classes can
     * be accessed by calling {@link #getClasses()}.
     * 
     * @param test
     *            the test to determine matching classes
     * @param packageNames
     *            one or more package names to scan (including subpackages) for
     *            classes
     */
    public void find(Test test, String... packageNames) {
        if (packageNames == null)
            return;

        for (String pkg : packageNames) {
            findInPackage(test, pkg);
        }
    }

    /**
     * Scans for classes starting at the package provided and descending into
     * subpackages. Each class is offered up to the Test as it is discovered,
     * and if the Test returns true the class is retained. Accumulated classes
     * can be fetched by calling {@link #getClasses()}.
     * 
     * @param test
     *            an instance of {@link Test} that will be used to filter
     *            classes
     * @param packageName
     *            the name of the package from which to start scanning for
     *            classes, e.g. {@code net.sourceforge.stripes}
     */
    public void findInPackage(Test test, String packageName) {
        packageName = packageName.replace('.', '/');
        ClassLoader loader = getClassLoader();
        Enumeration<URL> urls;

        try {
            urls = loader.getResources(packageName);
        } catch (IOException ioe) {
            if (logger.isWarnEnabled()) {
                logger.warn("Could not read package: " + packageName, ioe);
            }
            return;
        }

        while (urls.hasMoreElements()) {
            try {
                String urlPath = urls.nextElement().getFile();
                urlPath = URLDecoder.decode(urlPath, "UTF-8");

                // If it's a file in a directory, trim the stupid file: spec
                if (urlPath.startsWith("file:")) {
                    urlPath = urlPath.substring(5);
                }

                // Else it's in a JAR, grab the path to the jar
                if (urlPath.indexOf('!') > 0) {
                    urlPath = urlPath.substring(0, urlPath.indexOf('!'));
                }

                if (logger.isInfoEnabled()) {
                    logger.info("Scanning for classes in [" + urlPath + "] matching criteria: " + test);
                }
                File file = new File(urlPath);
                if (file.isDirectory()) {
                    loadImplementationsInDirectory(test, packageName, file);
                } else {
                    loadImplementationsInJar(test, packageName, file);
                }
            } catch (IOException ioe) {
                if (logger.isWarnEnabled()) {
                    logger.warn("could not read entries", ioe);
                }
            }
        }
    }

    /**
     * Finds matches in a physical directory on a filesystem. Examines all files
     * within a directory - if the File object is not a directory, and ends with
     * <i>.class</i> the file is loaded and tested to see if it is acceptable
     * according to the Test. Operates recursively to find classes within a
     * folder structure matching the package structure.
     * 
     * @param test
     *            a Test used to filter the classes that are discovered
     * @param parent
     *            the package name up to this directory in the package
     *            hierarchy. E.g. if /classes is in the classpath and we wish to
     *            examine files in /classes/org/apache then the values of
     *            <i>parent</i> would be <i>org/apache</i>
     * @param location
     *            a File object representing a directory
     */
    private void loadImplementationsInDirectory(Test test, String parent, File location) {
        File[] files = location.listFiles();
        StringBuilder builder = null;

        for (File file : files) {
            builder = new StringBuilder(100);
            builder.append(parent).append("/").append(file.getName());
            String packageOrClass = (parent == null ? file.getName() : builder.toString());

            if (file.isDirectory()) {
                loadImplementationsInDirectory(test, packageOrClass, file);
            } else if (isTestApplicable(test, file.getName())) {
                addIfMatching(test, packageOrClass);
            }
        }
    }

    private boolean isTestApplicable(Test test, String path) {
        return test.doesMatchResource() || path.endsWith(".class") && test.doesMatchClass();
    }

    /**
     * Finds matching classes within a jar files that contains a folder
     * structure matching the package structure. If the File is not a JarFile or
     * does not exist a warning will be logged, but no error will be raised.
     * 
     * @param test
     *            a Test used to filter the classes that are discovered
     * @param parent
     *            the parent package under which classes must be in order to be
     *            considered
     * @param jarfile
     *            the jar file to be examined for classes
     */
    @SuppressWarnings("resource")
    private void loadImplementationsInJar(Test test, String parent, File jarfile) {

        try {
            JarEntry entry;
            JarInputStream jarStream = new JarInputStream(new FileInputStream(jarfile));

            while ((entry = jarStream.getNextJarEntry()) != null) {
                String name = entry.getName();
                if (!entry.isDirectory() && name.startsWith(parent) && isTestApplicable(test, name)) {
                    addIfMatching(test, name);
                }
            }
        } catch (IOException ioe) {
            logger.error("Could not search jar file '" + jarfile + "' for classes matching criteria: " + test + " due to an IOException", ioe);
        }
    }

    /**
     * Add the class designated by the fully qualified class name provided to
     * the set of resolved classes if and only if it is approved by the Test
     * supplied.
     * 
     * @param test
     *            the test used to determine if the class matches
     * @param fqn
     *            the fully qualified name of a class
     */
    @SuppressWarnings({ "rawtypes", "unchecked" })
    protected void addIfMatching(Test test, String fqn) {
        try {
            ClassLoader loader = getClassLoader();
            if (test.doesMatchClass()) {
                String externalName = fqn.substring(0, fqn.indexOf('.')).replace('/', '.');
                if (logger.isDebugEnabled()) {
                    logger.debug("Checking to see if class " + externalName + " matches criteria [" + test + "]");
                }

                Class type = loader.loadClass(externalName);
                if (test.matches(type)) {
                    classMatches.add((Class<T>) type);
                }
            }
            if (test.doesMatchResource()) {
                URL url = loader.getResource(fqn);
                if (url == null) {
                    url = loader.getResource(fqn.substring(1));
                }
                if (url != null && test.matches(url)) {
                    resourceMatches.add(url);
                }
            }
        } catch (Throwable t) {
            if (logger.isWarnEnabled()) {
                logger.warn("Could not examine class '" + fqn + "' due to a " + t.getClass().getName() + " with message: " + t.getMessage());
            }
        }
    }
}